Screen panel

ABSTRACT

Screen panels are disclosed which are adapted to form a portion of a screening cylinder for screening fibrous material. The screen panels are unitary and made of wear-resistant material including a plurality of axially extending grooves on the outer surface of the screen panel, a plurality of slit-shaped screening orifices disposed at the bottom of the axial grooves, at least one support ring extending circumferentially across the surface of the screen panel and integral therewith, and a flange is formed at the sides of the screen panel so that the screen panels can be assembled together without the use of welding.

FIELD OF THE INVENTION

The present invention relates to a screen for screening fiber material.More particularly, the present invention is directed to a screen panelfor such a screen.

BACKGROUND OF THE INVENTION

During the screening of fiber material, such as fiber suspensions ofcellulosic material, the object is generally to separate coarseparticles in the form of shives, fiber bundles or other impurities fromthe fiber material. The screening is usually carried out in a screenwith a screening cylinder, which can be stationary or rotary. Thescreening cylinder is generally provided with holes or slits, throughwhich the fiber, but not the impurities, can pass.

Screening cylinders of this type are usually manufactured by drillingholes or milling slits in a metal sheet, which is then formed into acylinder. In order to obtain an open area, i.e. that portion of thecylinder surface which is perforated as much as possible, the holes orslits must be arranged in a tight relationship. At the same time, thestrength of the cylinder must be maintained. This therefore requireshigh precision work.

Particularly during the manufacture of slitted cylinders, which incertain cases are more advantageous than cylinders with holes which aredrilled, difficulties concerning the strength arise, because thematerial between the slits will become rather thin. The slits,therefore, must be made short and arranged at a certain relationshipfrom each other. This, in turn, results in a certain restriction of theopen area.

One way to solve this problem is to form the cylinder from a greatnumber of bars, which are kept in place by annular strips. This,however, is a complicated and expensive way of manufacturing a screeningcylinder. It is, furthermore, difficult to provide the slits with auniform width across the entire cylinder.

SUMMARY OF THE INVENTION

In accordance with the present invention, this and other difficultieshave been solved by the invention of a screen panel adapted toconstitute a portion of a screening cylinder for the screening offibrous material, the screen panel comprising a unitary screen panel ofwear-resistant material having a first surface, a second surface, anupper edge, a lower edge, and a pair of side edges, the first surfaceincluding a plurality of axially extending grooves, a plurality ofslit-shaped screening orifices disposed at the bottom of the pluralityof axially extending grooves, at least one support ring extendingcircumferentially across the first surface and being integral with thescreen panel, and assembly means for assembling the screen panel intothe screening cylinder without the use of welding. Preferably, thescreen panel includes a plurality of the support rings.

In accordance with one embodiment of the screen panel of the presentinvention, the screen panel includes a plurality of recesses on thesecond surface of the screen panel at a location directly in front ofthe plurality of axially extending grooves.

In accordance with another embodiment of the screen panel of the presentinvention, the plurality of slit-shaped screening orifices have a slitwidth of between about 0.5 and 1 mm.

In accordance with another embodiment of the screen panel of the presentinvention, the assembly means comprises at least one flange formed onone of the pair of side edges. Preferably, the assembly means furthercomprises additional fastening members disposed along the top and bottomedges of the screen panel.

According to the present invention, these problems are thus solved byforming the screen from a number of screen panels, which together form ascreening cylinder, i.e. each screen panel constitutes one portion ofthe circumference of the screening cylinder. One screen panel canpossibly extend around the entire circumference of the screeningcylinder. The screen panels are manufactured individually by beingformed in one piece, whereafter the screen orifices are provided in thepanels. Several panels are thereafter assembled to form a screeningcylinder.

The forming of the panels can be carried out by casting, compressionmolding or the like, of a material which is a suitable wear-resistantmetal alloy or ceramic material, for example alumina. Such material isnot weldable. The screen panels, thus, must be joined together withoutwelding.

Each panel is formed with a curvature radius, which substantiallycorresponds to the radius of the screening cylinder. The panel is alsoformed with a great number of substantially axial grooves and a numberof support rings, which extend substantially in the circumferentialdirection. These support rings are formed as an integral part of thepanel. These rings are located on the same side of the screen panel asare the grooves. On the opposite side of the panel recesses arepreferably formed, which are located directly in front of the grooves.The panel is also formed with edge flanges, by means of which severalpanels can be assembled in the circumferential direction. Fasteningmeans can be formed along the curved edges for attaching the panelsaxially to one another.

After their forming, the panels are provided with screening orifices,which are cut in the form of substantially axial slits. This ispreferably carried out by precision grinding, by means of which a slitwidth of about 0.1 to 1 mm can be obtained. The slits are placed inrelation to the grooves, preferably at the bottom thereof. The screeningorifices are cut out from the opposite side in relation to the groovesand support rings, so that the slits extend through the panel to thebottom of the grooves, but not through the support rings. Thereby amaximum open area is obtained, and at the same time the strength of thescreen panel is maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail in the followingdetailed description, with reference to the accompanying Figuresillustrating an embodiment of the screen panel according to the presentinvention, as follows:

FIG. 1 is a front, perspective view of a screen panel according to thepresent invention;

FIG. 2 is a front, elevational view of the screen panel shown in FIG. 1;

FIG. 3 is a side, elevational, sectional view of the screen panel ofFIG. 2, taken along line III—III thereof; and

FIG. 4 is a side, elevational, sectional view of the screen panel ofFIG. 2, taken along line IV—IV in FIG. 2.

DETAILED DESCRIPTION

The screen panel 1 shown in FIG. 1 constitutes a portion of the jacketsurface of a screening cylinder, as seen in the circumferentialdirection. The entire screening cylinder is formed by the assembling ofa plurality of screen panels. Each screen panel, therefore, is formedwith edge flanges 2 for attachment by bolts or in some other way, butnot by welding. For assembling these panels axially, the panels areprovided with fastening means 3, also along the curved edges for beingattached together without welding.

Each panel is preferably formed by casting according to the shellmolding method, precision casting or centrifugal casting. The castingmold has the shape desired for the finished panel. In FIG. 4 the profileof the screen surface is shown with deep axial grooves 4 on one side andrecesses 5 on the other side. The panel also includes a number ofsupport rings 6, which extend substantially in the circumferentialdirection. The support rings are formed in one piece with the panel andextend along the entire surface of the panel on the same side as thegrooves 4.

After casting, a certain adjustment in the shape of the panel can bemade by bending. The panel is provided with screening orifices in theform of slits 7 at the bottom of the grooves 4. The slits 7 are cut byprecision grinding, electronic cutting or another precision methodwhereby a slit width of from about 0.1 to 1 mm can be obtained. Thesurfaces of the screening orifices can be improved, and the slit widthcan be adjusted, by polishing. The slit width can also be adjusted byafter-bending the panel.

The present invention demonstrates that a slitted screening cylinder canbe manufactured with great dimensional accuracy and with a great openarea without deteriorating its strength. The screen panels are assembledto a cylinder in a suitable manner, for example by means of screwunions, holding rings, or in some other way.

A screening cylinder manufactured from screen panels according to thepresent invention can be provided with high precision and greatstrength. It is easy to mount and can be formed of highly wear-resistantmaterial, ensuring long service life. Due to the high precision of thescreening orifices, the screening result can also be improved.

The support rings 6 yield a substantial increase in strength of thescreen panel and offer the possibility of high dimensional accuracy ofthe slits 7, while at the same time the open area can be maximized. Thesupport rings also imply that the grooves 4 and slits 7 can have adirection deviating from the axial one without deteriorating thestrength.

The wear-resistance of the screen panel can be improved by surfacetreatment of the edge flanges 2 and fastening means 3 in a suitablemanner, for example by nitration or hardening.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A screen panel adapted to constitute a portion ofa screening cylinder for the screening of fibrous material, said screenpanel comprising a unitary screen panel of wear-resistant materialhaving a first surface, a second surface, an upper edge, a lower edge,and a pair of side edges, said first surface including a plurality ofaxially extending grooves, a plurality of slit-shaped screening orificesdisposed at the bottom of said plurality of axially extending grooves,at least one support ring extending circumferentially across said firstsurface and being integral with said screen panel, and assembly meansfor assembling said screen panel into said screening cylinder withoutthe use of welding.
 2. The screen panel of claim 1 including a pluralityof said support rings.
 3. The screen panel of claim 1 including aplurality of recesses on said second surface of said screen panel at alocation directly in front of said plurality of axially extendinggrooves.
 4. The screen panel of claim 1 wherein said plurality ofslit-shaped screening orifices have a slit width of between about 0.5and 1 mm.
 5. The screen panel of claim 1 wherein said assembly meanscomprises at least one flange formed on one of said pair of side edges.6. The screen panel of claim 5 wherein said assembly means furthercomprises additional fastening members disposed along said top andbottom edges of said screen panel.